US officials argue industry can help satellite ATM advance

Pressured
by civil aviation interests to intensify their efforts to make space-based air
traffic management (ATM) a reality, US government officials respond that the
aviation industry too has major responsibilities in advancing use of the
technology.

Prime
among the ways in which the aviation industry can assist the US government in
developing satellite-based ATM to operational fruition is in making sure users
equip their aircraft early, says Volpe Transportation Research Center engineer
Karen Van Dyke.

“The
industry needs to support the government by equipping,” she declared today at
an Air Traffic Control Association symposium on space-based ATM.

But
some industry figures do not agree, arguing that it is more the responsibility
of the US government to persuade the civil aviation industry of the business
benefits of equipping their aircraft for satellite navigation than it is for
the industry to equip in an informational vacuum.

“In
itself the industry can do little to push this peanut uphill,” says the Air
Transport Association’s vice president for ATM, Jack Ryan. “The government
asks, ‘When are you going to equip?’ But there’s an obligation on [both] the
government and industry – the government first – in this chicken-and-egg.”

Ryan
proposes a solution. “The government needs to hold some industry days soon to
report on its operational evaluations of [the] Safe Flight 21 [program]. It
needs to talk to operators so they can recognize advantages, then agree on an
installation date and codify it through an NPRM (notice of proposed
rulemaking). In my personal opinion, voluntary equipage doesn’t work.”

The
FAA’s associate administrator for research and acquisition, Steve Zaidman,
argues that this is not entirely fair. “There has to be some recognition that
applications evolve,” he says. “The industry has to be a little more formal as
a group in its business decisions. There needs to be additional business-case
thinking from the industry.”

Most
importantly from the FAA’s viewpoint, says Zaidman, the US civil aviation
industry needs to focus on how it will handle in equipment terms the
transitional period from traditional ATM methods and technologies to the
space-based ATM navigation and communications technologies now rapidly nearing
fruition.

He
says the most difficult problem for the FAA in making the move from traditional
ATM to space-based ATM is that, “the industry also includes, for us, the
military and general aviation”.

Zaidman
declares: “That’s the hardest part for us. There is no single requirement and single
ability to pay [for use of the system]. There is no single, one-size-fits-all
treatment by equipage.”

But
Van Dyke believes that, by inaction, the navigational equipment manufacturers
have been making the job of the FAA – and other agencies internationally - in
developing satellite-based ATM more difficult.

She
says the manufacturers have dragged their feet on development of new GPS
receivers to take full advantage of the US government’s decision to remove the
deliberate timing error from the GPS signal in 2000. The US government had
formerly overlaid this varying error on civil GPS signals to make it impossible
for potential enemies to use GPS for positional data to guide weapons
accurately against US targets.

Van
Dyke explains that the control circuits for existing civil aircraft GPS
receivers, built to the TSOC 129 technical standard, are hard-wired to apply
automatically a 33m pseudo-range error to average out the deliberate selective
availability (SA) error.

The
SA error makes it impossible for a GPS receiver to provide positional data
accurate enough to use GPS for precision landing approaches, one of the most
important future tasks for any space-based ATM system.

Another
problem, she says, lies in the receiver manufacturers’ short-sighted decision
not to develop new aviation GPS receivers until the FAA proves that the signal
integrity of its Wide Area Augmentation System (WAAS), a nationwide GPS signal
augmentation system, is sufficient to allow aviation operators to use WAAS for
precision navigation.

Van
Dyke says the software in each existing TSOC 129 receiver includes the receiver
autonomous integrity monitoring (RAIM) algorithm that constantly checks the
integrity of the GPS signal. However, if the TSOC 129 receiver’s RAIM function
determines the GPS signal has lost integrity, it automatically turns the system
off, making the aircraft unable to use GPS for precision navigation.

Now
there are new technical design standards, TSO 145 and TSO 146, for GPS
receivers that on one hand do away with the 33m pseudo-range error and on the
other do not turn the receiver off if its RAIM function detects a loss of
signal integrity.

Instead,
the receiver software determines which of the several signals from different
GPS satellites has lost integrity, and automatically excludes just that signal.
In almost all cases loss of signal from just one satellite will not be critical
enough to affect the receiver’s overall position-calculating accuracy, says Van
Dyke, “so you can isolate the faulty satellite and continue navigating”.

But
despite these GPS receiver design advances, manufacturers have done nothing yet
to incorporate them into actual receiver designs. She believes this is a poor
business decision by the manufacturers, particularly when trying to win sales
of their GPS receivers internationally.

“If
you have RAIM, there is nothing more you need – there is no need to wait for
WAAS to be commissioned,” says Van Dyke.